Tap chi Khoa hoc va Cong nghe Bien; Tap 14, S6 2; 2014: 139-148 ISSN: 1859-3097 http://www.vjs.ac.vn/index.php/jmst
DAC mtM BIEN DONG DONG C H A Y VUNG VEN B 6 CHAU THO SONG HONG - KET QUA NGHIEN CUtT TU" ]Vr6 HINH 3D
Vu Duy VTnh*, Trdn Due Thanh
Vien Tai nguyen va Mdi trudng bian-Vien Han lim Khoa hpc vi Cdng nghe Viet Nam Email: [email protected]
Ngay nhin bai: 6-1-2013
TOM TAT: Bdi viet ndy trinh bdy cdc ket qud dp dung mo hinh todn hgc 3 chieu (3D) de nghien cicu ddc diem bien dpng dong chdy d viing ven bd chdu tho song Hong. Trong nghien cuu ndy, mgt mo hinh 3 chieu da dugc thiet lap vdi 4 lap do sdu (he toa do a). So lieu dua vdo tic cdc bien md phia bien co dugc thong qua su dyng phuang phdp ludi long (NESTING) ciing mgt mo hinh tinh rgng han d phia ngodi. Mo hinh da duac hieu chinh kiem chimg vdi so lieu do muc nude tai Hon Ddu vd ddng chdy tgi mot so diem (Ba Lat, Nam Trieu) trong khu vuc nghien cicu. Cdc kit qud tinh todn da cho thdy cdc ddc diem bien dgng theo khong gian vd thai gian ciia trudng dong chdy long hgp vd ddng du d khu vice ven bd chdu tho sdng Hong, trong do da chi ra cdc vai trd khdc nhau ciia dao dgng muc nude - dong trieu, dong chdy song, trudng gio - dong gradien vd dong chdy mat do (khong tinh den vai tro ciia dong chdy do sdng).
Tii- khda: Dong chdy, mo hinh, ddng du, thuy dgng luc, ven bd chdu tho song Hong.
MO DAU
Viing ven bd chau thd sdng Hdng (CTSH) la nai cd dieu kien ddng lye phuc tap vdi su inh hudng va tuang tac ddng eiia cac yau td khac nhau nhu ddng chay tii' cic sdng dua ra kha ldn, dao ddng mue nude (DDMN) mang tinh chit nhit trieu dien hinh, dp cao thiiy triau cue dai cd tha len tdi 4,0 m [5] va dieu kien song gid ludn bian ddi manh theo thdi gian.
Cha do thuy dpng luc (TDL) d day co vai tro rat quan trgng trong viec van chuyen biin cat, bien dpng dja hinh cQng nhu khi nang phat tan cie chit gay d nhiem tir viing ven bd ra phfa ngoai bian [14, 15, 17]. Chinh vi vay, dac diem bian dpng ddng chay d khu vuc niy da dugc quan tam nghian ciru d nhieu khia canh khic nhau nhu phan tich tir sd lieu do dac khao sat va md hinh toan [7, 14, 16, 17]. Nghian cuu nay dugc thuc tran cd sd ip dun§ mgt md hinh 3 chiau (3D) de md phdng cac dieu kien TDL d
viing ven bd CTSH, qua dd danh gia eac dac diam bien ddng cua ddng chay theo khdng gian va thdi gian d khu vuc.
TAX LIEU VA PHUCfNG PHAP Khu vuc nghien ciiu nam trong khoang tpa do 19"! 5' - 21°00' vT do Bic vi 105''48' - 106^57' kinh dg Dong, thudc viing bien ven bd Tiy vinh Bac Bd, phia Bac Viet Nam, each Ha Npi khoang iOO km ve phia Dong. Day la khu vu'c CO che do thiiy trieu mang tinh chat nhat triau deu vdi bien dp khi ldn. Dp ddc day bian tuang doi ldn d khu vuc cira Ba Lat nhung nhd d viing cua Bach Dang va cua Day. Khu vue chiu anh hudng manh cua cac khdi nude tir he thdng sdng Hong-Thai Binh dua ra, nhung tii luang nude phin phdi khdng deu trong nam, ehii yau tap trung vao cac thang miia mua [13, 14], Khu vuc niy cQng chiu su ehi phdi ciia he thdng gid mua Ddng Bac trong miia khd va gio miia Tay Nam trong mua mua.
Vu Duy VTnh, Tran Diic Thanh Tai lieu.
Trong nghien cuu nay, cac dii lieu da dugc thu thip xir ly khi dong bd va he thdng:
So lieu dp sau va dudng bd ciia viing ven bd CTSH duac sd hda tir cac tir eac ban do dia hinh UTM he tpa do dia ly VN 2000 ty le 1:50.000 va 1:25.000 do Cue Do dae Ban do (Bp Tai nguyen va Mdi trudng Viet Nam) xuat bin nam 2005. Do sau cua khu vue phia ngoai va Cling nhu viing vinh Bac Bd dugc sir dung tir ea sd dii tieu GEBCO -1/8 cua Trung tam tu lieu Hai duang hgc Vuong qudc Anh. Day la so lieu dia hinh cd dp phan dai 0,5 phut dugc xir ly tir inh ve tinh ket hpp vdi cac sd lieu do siu [8].
Sd lieu khi tupng gdm cic sd lieu gid quan trie trong nhieu nam d Tram Hii van Hdn Diu va Bach Long VT da dugc thu thap va xu ly, trong dd cd sd lieu do dac vdi tan suat 6h/lan trong thdi gian thang 2-3 va thing 7-8 nim 2009.
Sd lieu ve DDMN d viing ven bd CTSH dugc thu thap de hieu chinh md hinh va cung cap cho cac dieu kien bian md phia bian. Sp lieu muc nude da hieu chinh md hinh la eac ket qua do dac muc nude (Ih/lin) tai Hdn Dau trong nhiau nim. Cac sd lieu DDMN tai cac bian md phia bien ciing da duge thu thap xir ly da thiat lap cie dieu kien bien md phia bian eua md hinh TDL. Tai eac diem bian md gin bd, cac sd lieu duge thu thip xir ly dua tren cac ket qua quan trie. Cac hang sd dieu hda thuy trieu d phia ngoai xa_ bd dugc thu thip tir ca sd dii liau cac hang sd diau hda thuy triau FES2004 cua LEGOS va CLS [6].
Sd lieu ve nhiet dd va do mudi nude bien d viing cira sdng ven bd CTSH va vinh Bac Bp dupc thu thap tir cac ket qui nghien cim lien quan trong khu vuc. Ngoai ra, da su dung cho md hinh tinh eho cae dieu kien bian md phia bian, so lieu nhiet dp va dp mudi nude bien dupc thu thap tir eo sd dij lieu WOA09 [18].
Sd lieu ddng chiy do dac tai mgt sd vi tri khao sat trong khu vuc nghien cuu ciia mgt so de tai du in viing eira sdng ven bd CTSH eiing da dugc thu thip xu ly de phuc vu hieu chinh kiam chirng dp tin cay cua md hinh TDL tir cae da tai hgp tic theo Nghi dinh thu Viet Nam-Bi.
"Phdt triin he thdng mo hinh thiiy nhi$t dong luc-sinh thdi hien phuc vu nghien cuu vd qudn ly tdi nguyen biin viing ven ba Viet Nam" va de tai Dd tai ddc lap cap Nha nude "Nghien cm, ddnh gid tdc dgng cUa cdc cong trinh ho chica thuang nguon den dien bien hinh thdi vd tai nguyen - moi trudng viing cira song ven biin dong hdng Bdc Bg".
Phuorng phap
Phuang phdp GIS de so hda va xu ly so Heu dia hmh. Tir cac ban do dia hinh ty le l:'50.obo va I :25.000 do Cue Do dac Bin do xuit bin vdi he toa do UTM-VN2000 d viing ven bd CTSH, da su dung cac phan mem Maplnfo va Arcview de sd hda vi tai thinh cac file dia hinh sd d khu vuc nghien cuu. Cacjihin mam GIS cung dupc diing de ldng ghep sd lieu dia hinh d viing ven bien vdi sd lieu dja hinh trong GEBCO -1/8 d viing ngoai khai.
Phuong phdp khai thac so lieu tir ca sd du;
lieu nhiet mudi WOA09 va ca sd du lieu thuy trieu FES2004 nhim cung cap sd lieu can thiet de xic dinh cac dieu kien bien md nhiet - muoi cho md hinh TDL viing ngoai khai (vdi ludi tinh thd) dugc luu trii d dang file Netcdf
Phuang phdp ludi long (NESTING) duac sir dung trong nghian cmi niy de tao ra cac diau kien bien md phia bien eua md hinh. De tao cac file sd lieu cho dieu kien bian md phia bien cua md hinh vdi ludi chi tiet (cho viing ven bd CTSH), mdt md hinh vdi ludi thd hon cung thdi gian tinh toan, cung kieu ludi tinh d phia ngoai vimg nay da dugc thiet lap. Md hinh ludi thd cd kich thudc 424 x 150 diem tinh va su dung he ludi cong true giao. Cac d ludi co kich thude bian doi hi: 379,3 - 1.376,5 m. Theo chieu thang dung, md hinh nay dugc chia thanh 4 lap dp sau trong he tga do a. Bian md bien cua mo hinh nay dupe chia thanh nhieu doan khac nhau, mdi doan sii dung cac hang sd dieu hoa trong FES2004 va sd lieu nhiet mudi trung binh thing trong ca sd dir lieu WOA09 [18].
Phuang phdp irng dung md hinh todn Cac dieu kien TDL dugc md hinh hoa bang module Delft3d-Flow trong he thdng mo hinh Delft3d ciia Ha Lan. Md hinh nay cd the md phdng tdt diau kien TDL-sdng, van chuyen bim cat d viing cira sdng ven bd [2].
Dac diem bien dpng dong diay v ^ g ven bd ..
Md hinh TDL cho khu vuc cua sdng ven bd CTSH sii dung he ludi cong true giao cd pham vi viing tinh bao gdm cae vung nude ciia cac cua song Bach Ding, Cim, Lach Tray, Van Uc, Thai Binh, Tra Ly, Ba Lat, Ninh Ca va Day va phia ngoai cac cua sdng nay. Mien tinh cd kich thudc khoang 223 km theo chieu Ddng Bac - Tay Nam va 113 km theo chiSu Tay Bic - Ddng Nam, vdi dien tich mat nude khoang 18.357 km^ dugc chia thanh 617 x 235 dilm tinh, kich thudc cac 6 ludi bien ddi tir 187 m dan 750 m. Theo chieu thang diing, toan bg cdt nude dugc chia lam 4 Idp do sau theo he tpa dp o. Ludi dp sau dugc thiat lap tren ca sd ludi tinh va ban do dja hinh ciia khu vuc. Md hinh dugc thiet lap va tinh den ca cac qua trinh nhiet-mudi va anh hudng ciia sdng.
Md hinh TDL duoc thiat lap va chay vdi cac miia die trung trong nam: miia mua (thing 7-8 nam 2009); miia khd (thing 2- 3 nam 2009). Budc thdi gian chay eiia md hinh la 0,5 phut.
Diau kien ban diu cua eic kich ban hien tr^ng la cac ket qua tinh toan sau ngay cudi trong cac file restart ciia thang 2 (miia khd) vi thing 7 (miia mua). Sd lieu da cung cip eho cic bian md phia bian la kat qui tinh toan toan tu md hinh phia tigoai sau dd sii dung phuong phip NESTHD da tao cic file so lieu nhiet dp, dg muoi, mue nude tai cac diem bien. Day la cic so lieu d^ng limeserial vdi tin suit Ih/lin.
Doi vdi cac bian sdng, sd lieu dp mudi va nhiet do cho diau kien bien la cac dac trung trung binh thing. Luu lugng nude sii dung cho cae dieu kien bian sdng la cic chudi sd lieu duge tinh toan tir sd lieu do vai tin suit Ih/lan.
Cic ket qua tinh toan cua md hinh nhu m\rc nude (tai Hdn Dau) va ddng chay (tai Ba L^t va Nam Tri?u) da dugc hieu chinh va kiam chung thdng qua viec so sanh vdi sd lieu quan trie trong thdi gian tuang ling. Ddi vdi kat qui tinh toan DDIVIN cua md hinh, sau lin hieu chinh cudi ket qui so sanh cho thay da cd su phii hgp ca ve pha vi bien dd giiia sd lieu quan trie va tinh toan. He s6 tuang quan giiia muc nude quan trie va tinh toan trong miia khd vi miia mua lin lugt la 0,96 va 0,98. Sai sd binh phuong trung binh tuang u:ng tin lugt li 0,22 m va 0,20 m. Cac gia trj quan trie ddng chiy
dugc phan tich thanh cac thanh phan kinh hudng (U) va vT hudng (V) trudc khi so sanh vdi cac ket qua tinh toin tir md hinh. Sau lin hieu chinh cudi cung, cac ket qua so sanh cho thay giiia quan trie va tinh toan ddng chiy d khu vuc nay la phu hgp [17].
DAC DIEM BIEN DONG CUA TRU"C)fNG DONG CHAY VUNG VEN BOf CHAU THO SONG HONG
Bien dong cua tru-tfng dong chay theo khong gian
Tnrong ddng chiy viing ven bd CTSH ludn bien ddng theo khdng gian. Nhiing khu vuc cd van tdc ddng chay ldn la phia ngoai eiia Nam Trieu, Van Uc, Ba Lat va cira Diy. Tai day, gia tri van tdc ddng chiy phd bien dao ddng trong khoang 0,4 - 0,7 m/s, trong cic thdi diam chuyen tiep giiia pha triau lan hoac triau xuong, gii tri van tdc dong chiy cd tha len tdi tren 0,8 m/s. Cac khu vuc ed gia tri van tdc ddng chay nhd (dudi 0,2 m) la viing nude sit bd va xa cae cira sdng. Vao cac thdi diem nude rong, vin xuit hien ddng chay nhung chi tip trung d sit^ khu vuc ciia song phia trong vdi van tdc phd bian 0,3 - 0,5 m/s vao miia khd va 0,4 - 0,7 m/s vao miia mua. Trudng ddng chay vao thdi diam nude ldn eo gia tri van tdc khi nhd va chii yau xuat hien a viing phia trong ciia song vdi hudng tir bien vao sdng.
Hudng dong chay bien ddng theo pha dao ddng eua mue nude vdi hai hudng chii dao:
trong pha triau lan do su xim nhip cua cac khdi nude bian vao phia trong nan ddng chiy cd hudng chu dao la tir phia ngoai bien vao trong sdng; ngupc lai trong pha triau xudng, hudng ddng chiy chii yau tir trong song ra phia ngoai bien. Ngoii ra, d viing ven bd phia ngoai, ddng chay cd hudng chii dao la dge bd (hinh 1).
Van tde ddng chay eiing co xu hudng tang din tir phia ngoai bian vao cira sdng trong pha triau len va giam dan tir sdng ra phia ngoai bian trong pha triau xudng.
Phan bd theo khdng gian ciia trudng ddng chiy ciing tha hien anh hudng do bien ddng miia ciia tai lugng nude sdng dua ra. Pham vi inh hudng ciia cac khdi nude va ddng vat chat tir sdng dua ra viing ven bd kha manh va rpng ldn vao miia mua (hinh 1-b). Trong miia khd,
141
Vii Duy VTnh, Tran Ddc Thanh
do tai luang nude dua ra bien nhd len van tdc so vdi mua mua (hinh 1-a), the hien ro hon vao ddng chay d viing cua sdng va ven bd nhd ban pha trieu xudng.
Hinh 1. Phan bo truong dong chay tdng hop vung ven bd CTSH (a-trieu xudng-ting mat miia khd; b- trieu xuong - tang mat mua mua) Do dp sau khdng ldn nan, su phin ting ciia
trudng dong chay viing ven bd CTSH khi nhd.
Tinh toan vi phin tich cho thay su phin ting eiia ddng chay tang dan tii' viing eiia sdng ra viing bian phia ngoai, noi cd dp siu ldn hon.
Chenh lech ve gii tri van tde ddng chiy giiia cic ting vi su khac biet ve hudng chii yau xuat hien vao khoang dau pha triau lan hoac trieu xudng. Sir phan tang ddng chay ciing manh han trong nhiing ngay trieu cudng (chanh lech khoang 0,2 - 0,6 m/s giii'a tang mat va ting diy) va miia mua (so vdi miia khd).
Trong nhiing ngay triau kem, bien ddng eua trudng dong chiy tdng hpp ciing tuong tu nhu trong nhu'ng ngay trieu cudng nhung gia tri van toe cue dai d khu vue phia trong eac ciia sdng thudngco gii tri nhd hon (khoang 30-60%).
Phan bo theo khong gian eua trudng dong chay ddng nhat han vao nhiing ngay trieu kem va chanh lech gia tri van tdc ldn d mot sd khu vuc cue bo so vdi nen chung nhd ban so vdi nhiing ngay triau cudng. Vao pha triau len, trudng ddng chay hudng vao cae cira sdng cd gia tri rit nhd (dudi 0,2 nVs) so vdi ngay trieu eudng.
Trong khi do, vao thdi diem nude ldn ciia ngay
tneu kem, ddng chay hudng ra phia ngoii van cd gia tri kha ldn (khoing 0,1 - 0,3 m/s) d phia ngoai bian.
Thanh phin ddng du (residual current) c6 vai trd rat quan trpng quyat djnh xu hudng van chuyen vat chat cila mdi thiiy vuc [1, 9]. Trong viing nghien ciiu, cae thanh phan ddng du deu ed xu hudng di chuyen ve phia Tay Nam trong ca miia mua va miia khd (hinh 2). Van tdc dong du giam manh tir mat xudng day, phd bien trong khoang 0,1 - 0,3 m/s (ting mat) va 0,05 - 0,15 m/s (tang day). Khu vuc cd van tdc dong du ldn thuang nam trong khoing dp sau khoang 10 - 25 m vdi gii tri 0,3 - 0,5 m/s. Diy eiing la khu vue tap trung su di chuyan cua cac khdi nude sdng sau khi di ra khdi cira song dudi su anh hudng cua hieu irng Coriolis o viing bic ban ciu JI, 11]. Nhii'ng nghien ciru ve ddng thai phat trien cua cac khdi nude sdng da dupe thuc hien bing cac md hinh toan d viing CO bian dp trieu nhd [3,4] va d viing inh hudng thiiy triau manh [10], da chi ra rang cic khoj nude song dua trudc het se duoc md rdng ve phia bian va sau dd dich chuyan ve phia ben phai (d vimg bic ban ciu). Trudc khi khdi nude
nil
Dac diem bien dpng dong chay vung ven bd ..
sdng quay trd lai viing ven bd, chiing chech hudng lao thanh mot vet nude sdng ven bd. CI vung ven bd CTSH cd hai yeu td chinh inh hudng quyat dinh dan cudng do va hudng di chuyen cua ddng du li irng suit gid va cac khdi nude tir sdng dua ra. Su di chuyan ciia ddng du va phia Tay Nam trong miia mua (ngugc vdi hudng gid Nam, Tay Nam) da the hien uu the quyet djnh ciia eac khdi nude sdng den thanh
phan ddng du d viing ven bd so vdi inh hudng ciia ling suit gid (hinh 2-c, d). Trong khi dd, mac du dugc tang cudng hon (do trung vdi hudng gid) nhung van tdc ddng du miia khd nhd ban ro ret so vdi miia mua, do vai trd ciia cac khdi nude sdng suy giim manh (hinh 2-a, b). Nhiing ket qua danh gii nay kha phii hgp vdi nghien cuu lien quan da cd ve ddng du d khu vue nay [7, 16].
I
I
Hinh 2. Phan bo dong du vung ven bo CTSH trong miia kho
(Miia kho. a-tang mat, tnju cirong; b- tang mat, tneu kem; Miia mvra: c-tang mat, tneu cuang;
d- tang mat, trieu kem)
Vii Duy VTnh, Trin Due Thanh
Cic kat qui tinh toin ciing cho thay trong nhiing ngay trieu kem, van tdc ddng du thudng cd gia tri ldn ban vao nhirng ngay trieu eudng. Vimg nude cd van tdc ddng du ldn cung dugc md rgng ban vio nhiing ngiy triau kem (hinh 2).
Bien dong theo thoi gian
Cac kat qua phin tich cho thay bien ddng cua gia tri van tde ddng chay tdng hop d cie khu vuc khac nhau trong viing nghien eiiu deu phu thudc chat che vao DDMN trieu. Trong mgt chu ky trieu thudng xuit hien bdn cue tri
van tdc ddng chay: hai cue dai va hai cue tifiu.
Cue dai ddng vao niia cudi cua pha trieu xudng ldn hem cue dai ddng d nua diu pha trieu len.
Cd tha giai thich diau nay do sir tang cudng ciia ddng sdng ddi vdi ddng chay tdng hgp trong pha triau xudng va cung do vay ma van toe ddng chay vao miia mua thudng ldn han mua khd khoing 0,1 - 0,3 m/s. Do ldn ddng chiy va chanh lech giira cac tang cung thudng cd gia tri ldn ban d nhiing ngay tneu cudng va nhd hon vao nhiing ngay trieu kem. Tuy nhidn, sir bien ddng theo thdi gian cua ddng chay d mdi khu vuc lai cd nhung dac trung rieng.
27 28 29
Hinh 3. Bian dgng van tdc ddng chay va muc nude khu vuc phia ngoai ciia Bach Ding (a-thang 3/2009; b- thing 8/2009)
Khu vuc cira Bach Dang cd hinh thai gidng nhu dang vinh nua kin [12]. Vao miia kho, tai mgt sd thai diem trong nhdng ngay
triau cudng, v|n tdc ddng chiy phd bien 0,2 - 0,5 m/s, cd the dat gii tri 0,5 - 0,8 m/s va vito nhiing ngay triau kem, van tde ddng chay
Dac diem bien dpng ddng chay viing ven bd . khdng vugt qua 0,4 m/s (hinh 3-a). Vao mua
mua, van tdc ddng chay cd gii tri ldn ban, thudng trong khoang 0,55 - 0,9 m/s va dudi 0,4 m/s vao nhiing ngay trieu kem (hinh 3-b). O day, sir chenh lech gii tri van tdc ddng chay giiia tang mat vi day miia khd phd bien dudi 0,2 m/s, nhung vao miia mua (dac biet la nhirng ngiy trieu cudng), chanh lech niy ldn hon 0,3 m/s. Khoang thdi gian van tde ddng chay ldn va nho vao miia khd kha cin bang, nhung trong miia mua thdi gian ddng chay ed van toe ldn vao ky trieu xudng kha dai, den gan thdi diem nude rdng. Diau nay tha hien anh hudng ciia cac khdi nude sdng vio miia mua [15].
Khu vuc phia ngoai eua Ba Lat la viing bien thoang va ddng chiy d day khdng ehi chiu inh hudng ciia cac khdi nude tir sdng dua ra mi cdn cd vai trd cua ddng dge bd. Do v|y, mac dii bian ddng ddng chiy theo thdi gian van
the hien xu hudng chung ciia toan viing nhung cung cd nhiing die diem khac so vdi khu vuc cira Bach Dang. Van tde dong chiy d day ci trong miia mua va khd dau ldn hon d cira Bach Dang. Mac dii van cd su chanh lech dang ke ve ddng chay giira nhirng ngay trieu cudng vi trieu kem nhung da giam manh; tdc dd ddng chay manh nhat trong nhiing ngay triau kem hau hat dau ldn hon 0,6 m/s. Cue dai ddng chay thudng xuat hien sau thdi diem nude ldn khoang 2-4 gid, trong khi cue tiau ddng chiy xuat hien sau thai diem nude rdng khoang 2-5 gid. Sir chanh lech gia tri van tdc ddng chiy giira tang mat va day trong miia mua ciing ldn hon so vdi miia khd va ci hai miia deu ldn hon so vdi khu vuc cira Bach Ding. Vao nhiing ngay triau cudng miia mua, su phan tang eua dong chiy tang lan, chanh lech ting mat va day cd tha 0,4 - 0,6 m/s (hinh 4).
Hinh 4 Bien dgng vin tdc ddng chay va muc nude khu vue phia ngoai cira Ba Lat (a-thang 3/2009; b- thing 8/2009)
Vij Duy VTnh, Tran Due Thanh
Die diam bien ddng ddng chay d khu vuc phia ngoai cira Day theo thdi gian cd phin gidng vdi khu vuc ciia Ba Lat hon so vdi khu vuc cii'a Bach Dang, do ddng chay d day khdng chi chiu tic dpng eua cac khdi nude sdng dua ra ma cdn tuong tic vdi ddng dpc bd tir phia cira Ba Lat dua xudng. Tuy nhian, gia tri van tdc ddng chay d khu vuc nay nhd hon so vdi khu vuc cua Ba Lat, trong khoang 0,2 - 0,6 m/s vio miia khd va 0,2 - 0,8 m/s vao miia mua.
Van toe ddng chay ldn nhit vin xuit hien sau thdi diam nude ldn gidng cua Ba Lat, nhung xuat hien cham hon (sau thdi diam nude ldn khoing 3-6 gid). Ding chu y la trong miia mua ddng chay cue dai d khu vuc cua Day thutnig xuit hien sau thdi diern nude ldn sdm hem 2-3 gid so vdi miia khd, the hien su anh hudng ting cudng cua khdi nude dpc bd tir phia ciia Ba Lat di chuyen xudng (binh 5).
Hinh 5. Bien ddng van tdc ddng chiy vi muc nude khu vuc phia ngoai cua Day (a- thang 3/2009; b- thing 8/2009)'
KET LUAN sdng dua ra. Ddng chiy tdng hgp ludn bien ddng theo pha DDMN triau, tuy nhian do dac Phan bo va bien ddng theo khdng gian va dilm hinh thai dia hinh khac nhau nen vai tro thdi gian cua trudng ddng chiy tong hop d ciia DDMN dan bian ddng ddng chay cd sir viing ven bd CTSH phu thupc chat che vio khac biet dang ka giira cic khu vuc ven bd phia DDMN tneu va bicn ddng theo miia ciia ngudn Ddng Bic vi Tay Nam cua Ba Lat.
Dac diem bien ddng ddng chay viing ven bd . Su phan tang ve gia tri van tdc ddng chay
tang dan tir khu vuc ciia sdng (noi cd do sau nhd) ra khu vuc phia ngoai, giam dan tir khu vuc ciia Ba Lat len phia khu virc ciia Bach Dang d phia Ddng Bic va xudng khu vuc cira Day d phia Tay Nam. Theo thdi gian, su phan tang dien ra rnanh me hon vao miia mua vi nhiing ngay trieu cudng.
Cac khdi nude tir sdng Hdng-Thai Binh cd vai trd quan trgng ban ung suit gid den thanh phin ddng du d viing ven bd CTSH. Dong du cd xu hudng di chuyen ve phia Tiy Nam trong ea hai miia (miia mua va khd) va phd bian trong khoang 0,1 - 0,3 m/s (ting mat) va 0,05- 0,15 m/s (ting day). Khu virc xuat hien van toe dong du ldn thudng nam viing nude cd dg sau khoang 10 - 25 m d phia Nam cira Ba Lat. Gia tri van tdc dong du ldn ban vio miia mua va nhiing ngiy triau kem.
Loi cam un: Bai bao nay la mdt phan ket qui CLia da tai hgp tie nghien ciru giira Vien Tai nguyen vi Mdi trudng bian va Vien Nghian ciru vi su phat trien Phap, da tai VAST.HTQt.Phip.01/14-15. Cae tae gii xin chin thanh cam an su hd trp quy bau dd.
TAI LIEU THAM KHAO
1. Azam, M H., Elshorbagy, W.; Ichikawa, L;
Terasawa, T.; and Tagiichi, K., 2006. 3D model application to study residual flow Arabian Gulf Ej. Wtrwy., Port, Coastal and Ocean Engineering, 132, issue 5, 388-400.
2. Delft Hydraulics, 2003. Delft3D-FLOW User Manual; Delft 3D-WAVE User Manual.
3. Chao S., 1988. River-forced esluarine plumes. J Phys Oceanogr 18: 72-88.
4. Kourafalou V, Oey L, Wang J, Lee T.
1996. The fate of river discharge on the continental shelf modeling the river plume and the inner shelf coastal current. J GeophysRes 101.3,415-3,434.
5. Phgm Vdn Hudn, Nguven Tdi Hai. 2007.
Dao dpng muc nude bian ven bd Viet Nam Tap chi Khi tupng thuy van, sd 556, thing 4 - 2007. Tr. 30-37
6. Lyard F. F. Lefevre, T Letellier. and O.
Francis, 2006. Modelling the global ocean
tides: modern insights from FES2004.
Ocean Dynamics, 56: 394-415.
7. Manh D. Yanagi T, 2000. A study on the residual flow in the gulf of tonkin. J Oceanogr 56: 59-68.
8. Jone M. T, Raymond N, Cramer R. N., 2009. User Guide to the centernary edition of the GEBCO digital atlas and its datasels.
Natural environment research council.
9. Murphy. P.L. and Valle Levinson A., 2008.
Tidal and residual circulation in the St.
Andrew Bay system, Florida. Continetal shelf Research, 28, 2,678-2,688.
10. Ruddick K, Deleersnijder E, Luyten P. Ozer J., 1995. Haline stratification in the rhinemeuse freshwater plume: A three- dimensional model sensitivity analysis.
Cont Shelf Res 15: 1,597-1,630.
W.Pedlosky J.. 1987. Geophysical Fluid Dynamics, Springer, New York.
12. Trdn Dire Thgnh, Nguyin Hiru Cir, Dinh Vdn Huy, Biil5i Van Vugng, 2007. Cac thuy vuc ven bd bien Viet Nam. Tap chi Khoa hpc vi Cdng nghe bidn, 7( 1): 64-79.
13. Trdn Dice Thgnh, VU Duy VTnh, Yoshiki Saito. Dd Dinh Chiin, Trdn Anh Tii. 2008.
Budc dau danh gia anh hudng ciia dap Hoa Binh den mdi trudng trim tich ven bd chau thd sdng Hdng. Tap chi Khoa hgc va Cdng nghe Bien, Tip 8, sd 3. Tr. 1-16.
14. VU Duy VTnh, Nguyen Dice Cu, Trdn Dire Thanh, 2011. Anh hudng cua dip Hda Binh den phin bd trim tich la lung viing ven bd chau thd song Hdng. Ky yeu Hpi nghi Khoa hoc va Cdng nghe bien lin thir 5, tip 3. Dia chat, Dia ly- Dia vat ly. Nxb. Khoa hpc tu nhien va Cdng Nghe. Tr. 465-475.
15. Vu Duy VTnh, Trdn Dice Thgnh. 2012. Lfng dung md hinh toan nghien cim viing due cue dai d khu vuc cira sdng Bach Dang Tap ehi Khoa hpc va Cdng nghe bien, Tip 12, sd3. Tr. 1-12.
16 Vii Duy VTnh, Kalrijn Baetens. Patrick Luyten. Trdn Anh Tic. Nguyen Thi Kim Anh.
2013. Anh hudng eua gid be mat dan phan b6 dp man va hoin luu vimg ven bd chau
Vii Ehiy VTnh, Tran Due Thanh
thd sdng Hdng. Tap chi Khoa hpc va Cdng nghe bien,Tap 13, so 1. Tr. 12-20.
17. Vii Duy VTnh, Biii Van Vuang, 2013. Anh hudng ciia mdt sd yeu td khi tupng hai van den bian ddng dja hinh d i ^ viing ven bd chau thd Sdng Hdng. Ky yau Hdi thio Hdi nghj khoa hpc dia chat bian toim qudc lan
thu 2. Nxb. Khoa hgc tu nhien va Cong Nghe. Tr. 285-294.
18. World Ocean Atlas 2009. National Oceanographie Data Center. 30-03-2010.
http://wwTv. node, noaa .gov/OC5/WOA09/pr woa09.html. Retrieved 19-5-2010.
CHARACTERISTICS OF CURRENT VARIATION IN THE COASTAL AREA OF RED RIVER DELTA - RESULTS OF RESAERCH USING THE
3D NUIVIERICAL MODEL
Vu Duy Vinh, Tran Due Thanh Institute of Marine Environment and Resources - VAST
ABSTRACT: This paper presents some results of three dimension (3D) modelling application to research characteristics of field current variation in the coastal area of Red River Delta. In the study, a 3D numerical model was set up with four vertical layers (a coordinate system) The open sea boundary conditions of hydrodynamics model have been obtained by NESTING method from the same I model for the larger marine region Hydrodynamics model was calibrated and validated by measured data of water levels in Hon Dau National Hydrographic Station and data of currents in other sites (Ba Lat and Nam Tneu). In the studied results the temporal and spatial variation of total currents and residual currents in the coastal area of Red River Delta are obtained, in which the different roles of tidal oscillalions-lide currents, fresh water from river mouths, wind stress-gradient currents and density currents were recorded (the roles of wave induced currents are ignored).
Keywords: currents, modelling, residual currents, hydrodynamics, coastal area of Red River Delta.
